Question

如果查询找到角色“elite”

，我想检索帐户数组

我尝试

db.users.aggregate(
{ $match : { "account.role" : "Elite" } }
);

但我有所反对......

{
"_id" : ObjectId("7623902143981943"),        
"account" : [ 
    {
        "role" : "Elite",            
        "action" : [ 
            "create", 
            "read", 
            "update", 
            "delete"
        ],
        "extra" : {
            account:[1,2,3,4]
        }
    },
 {
        "role" : "User",            
        "action" : [ 
            "create", 
            "read", 
            "update", 
            "delete"
        ],
        "extra" : {
            account:[10]
        }
    }
],

}

如果是查询的肯定结果，我可以只检索额外的数组（帐号：[1,2,3,4]）吗？或者我必须解析收到的对象？（架构非常简化，但我有很多角色）

Answer 1

您必须使用$project和$unwind：

//Order of $unwind and $match matters
db.users.aggregate(
 {$unwind: "$account"},
 {$match : { "account.role" : "Elite" }},
 {$project : { "extra.account" : 1}}
);

<强>解释

$ unwind将数组拆分为不同的元素。看到

的效果

 db.users.aggregate({$unwind: "$account"})

然后你将元素与{“account.role”：“Elite”}匹配。见效果：

db.users.aggregate(
 {$unwind: "$account"},
 {$match : { "account.role" : "Elite" }}
);

然后你最终投射出所需的字段

db.users.aggregate(
 {$unwind: "$account"},
 {$match : { "account.role" : "Elite" }},
 {$project : { "extra.account" : 1}}
);

//You can also remove the _id filed (included by default with:
db.users.aggregate(
 {$unwind: "$account"},
 {$match : { "account.role" : "Elite" }},
 {$project : { _id: 0, "extra.account" : 1}}
);

OLD ANSWER

您必须使用投影： db.users.aggregate（ {$ match：{“account.role”：“Elite”}}， {$ project：{“extra.account”：1}} ）;

此外，如果您只是匹配文档，则无需使用聚合framewrok，您只需使用：

// No projection here
db.users.find({"account.role" : "Elite"})

或

// Only returns the _id field + "extra.account" field if exists. By default the _id field is included
db.users.find({"account.role" : "Elite"}, { "extra.account" : 1}) 

// Only returns the "extra.account" field if exists
db.users.find({"account.role" : "Elite"}, { _id: 0, "extra.account" : 1})

可以找到Mongodb文档here和here

检索特定字段Mongoose

1 个答案: